I can't narrow it down to just one single factor.

One thing that should be provided is a good ICO White Paper. What I expect to find there is:

-   A clear and precise explanation about the problem that is being addressed, and the proposed solution.
- Token: utility, real need for it, volume, strategy, operational usage.
- Team: Core team profile and experience, as well as board of advisors.
- Known Investors backing ICO (commited).
- Current and foreseeable partners.
- Roadmap: Phase and delivery clearness, and associated timeframe.
- How and when funds will be used during ICO development.
- ICO type, token sale process, soft/hard caps, anti-whale caps.

Regardless, I find that other factors weigh in significantly in the ICO selection decision process:
-   Uniqueness of the idea /competitors.
-   Scope of use: A global scope of use, with a broad potential is better than a niche utility token.
-   Pre-existence of a working viable and verifiable product (instead of starting from scratch).
-   What plans are drawn for the token in the exchanges (major exchanges should be a real goal ideally).
-   Hype, size of follower base, momentum.

Even with all the above and due dilligance, there is no certainty in hitting the jackpot whatsoever, but odds may be a little more in your favour.